Process for making laminated hardboard product



Feb. 9, 1960 w. A. COTTON PROCESS FOR MAKING LAMINATED HARDBOARD PRODUCT Filed Jul 1a, 1956 v a amid-k INVENTOR WILLIAM A. COTTON Y 4 in! lui lni Haul Iii!!! ATTORNEY United States Patent PROCESS FOR MAKING LAMINATED HARDBOARD PRODUCT William A. Cotton, Wilmette, Ill., assignor to Masonite Corporation, Laurel, Miss., a corporation of Delaware Application July 16, 1956, Serial No. 597,872

4 Claims. (Cl. 162-432) The present invention relates to the production of lignocellulose hardboard. More particularly, the invention relates to the production of two-ply laminated hardboard articles. Even more particularly the invention relates to a method of preparing laminated hardboard sheet products containing a major proportion of hydrolyzed redwood fiber. The invention includes both the laminated products and the method of their manufacture.

It has been known to the art for many years that there may be produced a desirable lignocellulose hardboard sheet product characterized by its having two smooth surfaces as well as by its outstanding physical properties. The method for the preparation of such a product is described and claimed in US. Patent No. 2,120,137 to Mason, issued June 7, 1938. The patent discloses the felting of a sheet of hydrolyzed lignocellulose followed by drying the sheet and thereafter subjecting it to consolidating temperature and pressure between two smooth press platens. The product, having two smooth surfaces, has had wide commercial acceptance for several years.

The manufacture of these prior art products, however, has been restricted to hardboard sheets about one-eighth inch thick or less. This practice has been due, largely, to manufacturing conditions which have made it more practicable to produce relatively thin sheets rather than hardboard about one-quarter inch thick. The conditions responsible are connected with the speed of formation of the lap, the uniformity of lap formation, and the pressing times involved in the manufacture of the prod,- ucts. It has therefore been commercially unfeasible to produce thicker sheet products in a single manufacturing operation.

It is a principal object of the present invention to provide a method for the preparation of two-ply laminated lignocellulose hardboard sheet articles in one manufacturing operation.

I It is another object of the invention to provide a method for laminating dry felted laps of hydrolyzed lignocellulose fiber without the use of additional bonding agents.

A further object of the invention resides in the provision of novel two-ply laminated hardboard sheet articles containing a major proportion of redwood fiber. Other objects of the invention will become apparent from the following detailed description of the invention.

Hydrolyzed redwood fiber, either alone or in admixture with other similarly hydrolyzed Wood fiber such as fir, gum, pine, or the like, is first suitably refined in Water slurry. Thereafter, the fiber is formed into a wet lap on a conventional modified Fourdrinier machine. As the lap travels along the forming wire screen it is subjected to suction following a travel period of free water drainage. The application of suction not only removes much of the water, but also serves to concentrate in the lower portion of the lap the fines material which is always present in hydrolyzed wood fiber. In the case retested Feb. 9, 1960 2 of redwood, the fines material is recognized as possessing outstanding adhesive qualities and the concentration of this material in the lower portion of the wet lap has been found to be of great importance in the succeeding steps of the present novel method.

At this point of formation of the wet lap it has been found desirable, in some instances, to add additional water to the top surface of the lap. The added water insures that substantially all of the soluble material present is flushed from theupper portion of the wet lap and concentrated in the lower portion thereof. Then the lap is squeezed between pressure rolls and dried in a conventional drying apparatus.

In following the novel method of the invention it is important that the substantially dried lap have a moisture content of from about 0.2% to about 2.0% prior to consolidation. Moisture contents below about 0.2% result in insuflicient consolidation of the fiber together with lowered and unacceptable bond strengths in the finished laminated articles. Moisture contents in excess of about 2.0% result in the formation of blisters in the laminated products as well as undesirably high densities.

Thereafter, the substantially dry laps are arranged in two-ply condition with the bottom lap surfaces in contact with each other. The two-ply stacks are then charged to the openings of a multiplaten press. The laps are consolidated at pressures of from about 1000 to about 1600 p.s.i. and at temperatures of about 390- 410 F. In pressing it is desirable, for example, to subject the laps to an initial pressure of about 200400 p.s.i. with frequent release of the pressure to allow escape of moisture and other volatile materials. This treatment, i.e. the intermittent release of pressure, is termed breathing and is effected at about 30 second intervals during the low pressure treatment. The higher pressure of about 1000 1600 p.s.i. is then applied to efiect consolidation and lamination of the laps. Ordinarily, the low pressure treatment will extend over 2 or 3 minutes and the higher pressure is applied for about 30 to about 120 seconds. Subsequent to the pressing cycle the press is opened and the laminated articles removed therefrom without cooling. 1

The laminated products, having twosmooth surfaces, have an average specifica gravity within the range of about 1.1-1.30, average bond strength of about 250- 400 p.s.i. and outstanding qualities as regards modulus of rupture and transverse strength properties. It is, of course, of outstanding importance that these properties are obtained without the employment of any added binding material in or between the plies in contrast to previous practice in preparing similar relatively low density laminates.

.In carrying out the novel method of the invention a principal critical feature resides in the step of arranging the two laps for consolidation with their bottom surfaces contacting each other. Wherethe laps are not so positioned there is not sufiicient adhesion between the laps to insure obtaining a dependable bond-therebetween. Another critical feature resides in the use of from about 100% to about by weight of hydrolyzedredwood fiber in forming the laps. --The fines material of woods other than redwood apparently does not possess similar outstanding adhesiveproperties and diminution of the redwood fines by exceeding the above stated limits results in undesirable laminates.

The novel steps of the invention which must, therefore, be followed may be outlined as follows, the outline being directed particularlytothe drawing in which:

Fig. 1 is a schematic diagram illustrating the formation of a wet lap, andthe dewaterin'gand drying thereof,

Fig. 2 is a sectional side elevation of two dried laps in position for pressing,

press in the where desired, by a shorter period at high pressure. Similarly, products having specific gravities over the entire range of about 1.1 to about 1.3 may be obtained by adjusting the consolidation cycle. While the preferred In the process therefore: specific gravity range lies within about 1.12 to- 1.18, hard- (1) A fibrous slurry is flowed onto a traveling screen board products having lower or higher densities are often forming a felted lap containing 75 %100% of hydrolyzed of great value in particular usages. The consolidation conredwood fiber, ditions hereinbefore given, however, are extremely criti- (2) The fines and water solubles are concentrated 1n cal. Lower temperatures and pressures are productive the lower p n of the lap y fl wing dditlonal water of products having little or no bond strength. Higher onto the Wetlap f a temperatures cause sticking of the products to the press The Wfit p P y (if-Watered y Suctloll means platens. Within the stated limits, however, and employand4by P2 E ing a major proportion of hydrolyzed redwood fiber, the 1 T 6 lap 15 m d to a moisture content of 15 art is presented with a novel and highly desirable method of re arin im roved laminat d hardboar oduct (5) Two such dried laps are then'arranged with the z g p e d pr S ig pi iz 223232313 3 2? :2; b 1. A method of preparing a laminated sheet product 3mm y of fibrous hydrolyzed redwood lignocellulose which compressing at about 1000-1500 ps1 pressure at about s F I prises felting a lap of sald lignocellulose from an aque- With more particular reference to the drawing in Fig. Gus slurry thereof partially dfjwatering Said flowing I the numeral 10 is a traveling wire screen of a Fouronto upper Surfa ce of sad lap a quantity of Water drinier machine 11 upon which an aqueous fiber slurry is silfficlent to Substamlany remove from the upper flowed to form the Wet lap 11 Additional Water is tron :of the lap the fines and water soluble material flowed onto the upper Surface of the wet lap 12 r therein and to concentrate said material in the bottom the weir l t. Thereafter, the wet lap passes over the pomon of the drymg i lap to a nightlife suction boxes 16 and between the pressure rolls 18. of about Z ari'angmgktwc 9 531d drled laps The partially dewatered lap is then traveled through a face to face re1at1onsh1p,the aces n contact with each conventional drier 20 and emerges therefrom as the dried other bemg the Ones contafmxig comemrated lap Two of these dried laps 22 are arranged, as ter1al, and thereafter consolidating said laps into a lami- Shown in p 2, with their bottom Surfaces in Contact nated sheet product by the application thereto of heat with each other. The laps 22 are then placed in the and Pressure' press 24, shown in Fig, 3, a d lid d to produce 2. A method of preparing a laminated sheet product the laminated hardboard product 26 illustrated in Fig. 4. offibrous hydrolyzed redwoed hgno'cenulose W The invention will be illustrated with more particw prises arranging in surface to surface relationship two larity by the data of the following tables. Table I prefibrous SPbSiflHtIaUY y 13135 of 831d llgnocfilluwse, Said sents the conditions under which the two-ply hardboards p hflvlllg been P p 111 Such manner as to concenwere made, while Table II presents the physical properties irate 111 0116 Surface thereof the 51168 material Prfisent of the products. It is to be understood, however, that therein, the surfaces in contact with each other in said the examples are given for illustrative purposes alone 49 arrangement being the ones containing the concentrated and the invention is to be limited only by the Scope of fines material, and subjecting said laps containing not the appended claims. more than about 2.0% moisture to pressure of about Table I Time Time Thick- Oonsoli- Low under Breathes High under Moisture Percent Sample No. ness of dation Pressure Low @30 sec. Pressure High in Red- Produet, Temp. (p.s.i.) Pressure Intervals (p.s.i Pressure Sample wood inches F.) (Seconds) (Percent) an: 390 200-350 2.5 4 1,000 30 1.0 100 Vt 405 200-350 3.0 5 1,250 00 0.5 100 as 395 200-350 4.0 0 1,000 0.2 100 $4 400 200-350 3.0 5 1,600 45 2.0 80 V 34 410 200-350 3.0 5 1, 500 90 1.5 80

Tablell 1000-1600 p.s.i. and a temperature of about 390- 410 F. for a period of time sufficient to laminate said Sample No. Specific M,O R Bond of fibrous hydrolyzed lignocellulose which comprises Gravity Strength 0 laps into a consolidated sheet product.

' 3. A method of preparing a laminated sheet product 1 3 588 felting a lap of said lignocellulose containing a major 1:14 7i 000 310 proportion of redwood fiber from an aqueous slurry $2 $88 2, 8 thereof, applying suction to the bottom of said lap, drying the lap to a moisture content of about 0.2% to about 2.0%, arranging two of said dried laps with their bottom surfaces contacting each other, and thereafter consolidating said laps into a laminated sheet product by the application thereto of heat and pressure.

4. A method of preparing a laminated sheet product of fibrous hydrolyzed lignoceliulose together with the fines and water soluble material formed during hydrolysis which comprises felting a lap of said lignocellulose containing a major proportion of redwood fiber from an aqueous slurry thereof, concentrating the said material in the bottom portion of the wet lap by the application of suction thereto followed by the application of pressure, drying the wet lap to a moisture content of about 0.2% to about 2.0%, arranging two of said dried laps 1,707,333 Traquair Apr. 2, 1929 with their bottom surfaces contacting each other, charg- 5 1,730,849 Hinde Oct. 8, ing the two laps toa heated press opening, subjecting 1,884,563 Carson Oct. 25, 1932 the laps to pressure of about 1000-1600 p.s.i. and a temv 1,951,017 Hatch Mar. 13, perature of about 390410 F. until said laps have be- 1,995,145 Frost Mar. 19, come consolidated and laminated, and thereafter remov- 2,098,733 Sale Nov. 9, ing the laminated product from the press opening while 10 2,120,137 Mason June 7, still hot. 2,380,214 Burrell July 10,

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF PREPARING A LAMINATED SHEET PRODUCT OF FIBROUS HYDROLYZED REDWOOD LIGNOCELLULOSE WHICH COMPRISES FELTING A LAP OF SAID LIGNOCELLULOSE FROM AN AQUEOUS SLURRY THEREOF, PARTIALLY DEWATERING SAID LAP, FLOWING ONTO THE UPPER SURFACE OF SAID LAP A QUANTITY OF WATER SUFFICIENT TO SUBSTANTIALLY REMOVE FROM THE UPPER PORTION OF THE LAP THE FINES AND WATER SOLUBLE MATERIAL THEREIN AND TO CONCENTRATE SAID MATERIAL IN THE BOTTOM PORTION OF THE LAP, DRYING THE LAP TO A MOISTURE CONTENT OF ABOUT 0.2-2.0%, ARRANGING TWO OF SAID DRIED LAPS IN FACER TO FACE RELATIONSHIP, THE FACES IN CONTACT WITH EACH OTHER BEING THE ONES CONTAINING SAID CONCENTRATED MATERIAL, AND THEREAFTER CONSOLIDATING SAID LAPS INTO A LAMINATED SHEET PRODUCT BY THE APPLICATION THERETO OF HEAT AND PRESSURE. 